Abstract
This article examines how digital terrain model (DTM) grid cell size influences rockfall modelling using a probabilistic process-based model, Rockyfor3D, while taking into account the effect of forest on rockfall propagation and runout area. Two rockfall sites in the Trenta valley, NW Slovenia, were chosen as a case study. The analysis included DTM square grid cell sizes of 1, 2, 5, and 10 m, which were extracted from LiDAR data. In the paper, we compared results of rockfall propagation and runout areas, maximum kinetic energy, and maximum passing height between different grid cell sizes and forest/no forest scenario, namely by using goodness-of-fit indices (average index, success index, distance to the perfect classification, true skill statistics). The results show that the accuracy of the modelled shape of rockfall propagation and runout area decreases with larger DTM grid cell sizes. The forest has the important effect of reducing the rockfall propagation only at DTM1 and DTM2 and only if the distance between the source area and forest is large enough. Higher deviations of the maximum kinetic energy are present at DTMs with larger grid cell size, while differences are smaller at more DTMs with smaller grid cell sizes. Maximum passing height varies the most at DTM1 in the forest scenario, while at other DTMs, it does not experience larger deviations in the two scenarios.
Highlights
Mountainous areas are prone to many mass movement processes, rockfalls being one of the most common [1]
We only used one digital terrain model (DTM) grid cell size, since we predicted the similar behavior with others, as well as we were only changing one parameter at the time, and it does not consider simultaneous variations between the parameters, which could result in different modelling success
Forest is not always as efficient at reducing rockfall propagation area, maximum kinetic energies, or maximum passing heights, especially if the forest is too close to the rockfall source area or the rockfall event is too large to be stopped by forest
Summary
Mountainous areas are prone to many mass movement processes, rockfalls being one of the most common [1]. Rockfalls can be an important threat to infrastructure, human life, and their property, since they are rapid processes with long runouts [3], and their instantaneous occurrence makes their temporal prediction practically impossible [4]. By quantifying the potential rockfall hazard, simulation models can be used for planning different protection measures (e.g., technical measures, natural-based solutions) that can significantly reduce the potential risk of rockfall occurrence in high-threat areas [7,8,9,10]. Forests provide a natural solution for protection against rockfalls in alpine regions [11,12], since they can significantly reduce the intensity (kinetic energy) and propagation probability of falling rocks [13,14,15]. Models that do consider the protection effect of forest can be used for mapping protection forest and quantifying its protection function
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